Fix javac build

Add --multi-dex to LOCAL_DX_FLAGS where it is enabled for jack.

Test: m -j ANDROID_COMPILE_WITH_JACK=false FrameworksWifiTests

(cherry picked from commit e874763180ecb2f7f1c35c3752bd147119ca204a)

Bug: 36902714
Change-Id: I922c04e733f21565ac7ae91ddb9d24dc982170cc
diff --git a/tests/wifitests/Android.mk b/tests/wifitests/Android.mk
index 5dbd756..29c6749 100644
--- a/tests/wifitests/Android.mk
+++ b/tests/wifitests/Android.mk
@@ -49,6 +49,7 @@
 LOCAL_JACK_COVERAGE_INCLUDE_FILTER := $(jacoco_include)
 LOCAL_JACK_COVERAGE_EXCLUDE_FILTER := $(jacoco_exclude)
 
+LOCAL_DX_FLAGS := --multi-dex
 LOCAL_JACK_FLAGS := --multi-dex native
 
 # wifi-service and services must be included here so that the latest changes